With the advent of the Occupational Safety and Health Act (29 USC 651 et seq.), the National Institute of Occupational Safety and Health (NIOSH) has recently proposed noise standards for various industries. The proposal for machines retains the 90-decibel noise limit for equipment already in use but limits any new machines to an 85-decibel level. For comparative purposes, normal vocal effort at 6 inches from the ear is interfered with by a noise level of 72 decibels. Shouting at 6 inches from the ear is interfered with by a noise level of the order of 89-90 decibels. It has been determined that noise levels of 90 or above for prolonged periods can be hazardous to workers. Because of the logarithmic nature of sound intensity, a relatively small change in decibel rating represents a large change in the sound intensity.
A principal source of noise in industries utilizing machine tools is in connection with single and multiple spindle machines utilizing bar stock including rods of circular or polygonal cross section, e.g. hexagonal cross section. These rods are normally provided in lengths of from 12 to 21 feet. The workpiece end is generally inserted into a spindle sleeve having a collet member for gripping the workpiece adjacent the tooling. The free extremity of the bar stock is generally supported in a tubular member. Feeding may be effected either from the distal extremity of the supporting tube as shown in U.S. Pat. No. 2,608,746 to Harney or at the machine extremity in known manners. The bar stock in the course of the operations performed thereon at the collet extremity may be rotated at relatively high speed. Various forces working on the bar stock length cause the material to whip or oscillate within the supporting tube. The resulting noise level or intensity may be sufficient to cause injury to the ears of workers unless means are provided for reducing such noise level.
Prior art workers, notably Tessky in his U.S. Pat. Nos. 1,786,876, 1,891,290, and 1,935,999, Corlett U.S. Pat. No. 2,534,811, and Lakins U.S. Pat. No. 2,933,173, have shown structures which have sought to achieve reduction in the noise level for bar stock feed tubes to single or multiple spindle machines. In general, these structures have comprised a tubular body having disposed in concentric relation therewith spring materials (see the Tessky patents) or coiled sheaths wrapped with fabric, felt cloth, or material of such sort as a cushion between the OD of the coiled material and the ID of the supporting tube (see the Corlett patent). Lakins has shown a pair of concentrically disposed tubes defining an annular space therebetween which is filled with a viscous material of a putty-like nature consisting essentially of a mixture of metallic salts and oil.
The present invention is an improvement on these prior art structures and is capable of effecting reductions in decibel intensity ratings of from 2 to 6 or more decibels. These reductions are sufficient to bring the performance levels of the improved devices to or below the standards set by NIOSH.